KOBOLD DON-H High-Pressure Oval Gear Flow Meter, 400 bar

Oval gear flow metering for viscous liquids at high pressure

The KOBOLD DON-H is a stainless steel oval wheel flow meter for clean, non-abrasive liquids from low to high viscosity, such as petroleum, oil, grease, fuels, pastes, chemicals and ink. It is a positive displacement meter: two oval gears pass a constant volume per rotation through a precisely machined chamber, magnets in the rotors give a high-resolution pulse output, and the reading does not depend on conductivity. It needs no straight inlet run or flow conditioning, which suits tight skid and hydraulic installations.

The DON-H handles up to 400 bar (200 bar for the CSA and IECEE variant) and +120 °C, with a repeatability of typically ±0.03 %. The DON-S version uses special-cut rotors with alternate tooth relief to cut the pressure drop by about 50 % for viscosities above 1000 cP.

Technical specifications

Viscosity, pressure drop and filtration

Pressure drop grows with viscosity and flow rate, and the datasheet gives curves for sizes x05 to x15 and for x20. For viscosities above 1000 cP the maximum flow rate is reduced by a multiplier, for example 0.5 for a standard rotor at up to 2000 cP, and the datasheet example derates a DON-S20 on 8000 cP oil from 40 l/min to 20 l/min. Special cut rotors are less accurate below 1000 cP, so use the standard rotor for thin liquids.

Pressure surges above 3 bar at start-up can block the gears, especially in sizes x05 to x15, so start systems gradually and fit the recommended filter. When using the reed output the liquid temperature must not change faster than 10 °C per minute.

Ordering the DON-H

The order example is DON-H10H R1 1 H0 M 0: the model and range (05, 10, 15 or 20; H for stainless steel in litres or G in gallons), connection, O-ring material, electronics, cable entry and option. The U-PACE electronics code CT carries cCSAus and IECEE CB-scheme approval and an M12 plug. A battery version without calibration certificate exists for the Z-electronics.

Confirm before ordering: the viscosity at operating temperature, the maximum pressure including surges, the O-ring compatibility with the liquid, the required Ex marking, and whether l/min or GPM nameplate and calibration are needed.

How the KOBOLD DON-H works

The liquid pushes two oval gears around inside a precisely machined chamber. Each turn passes a fixed volume of liquid. Magnets in the rotors give a pulse for each turn, so the pulse count is a direct measure of volume.

Where the DON-H is used

• Hydraulic systems
• Fuel and oil metering
• Grease and paste lines
• Chemical dosing
• Ink supply lines

Selection checklist for the DON-H

• Flow range
• Liquid viscosity
• Operating pressure
• Medium temperature
• O-ring material
• Process connection
• Pulse output type
• Electronics option

Installation, commissioning and maintenance notes for the DON-H

Fit a filter ahead of the meter and keep the liquid clean. No straight inlet run is needed. Connect the pulse output to the counter or electronics and check the flow reading against a known volume. Clean the meter if the filter has let particles through.

Requesting a quotation for the KOBOLD DON-H

Please send the liquid, the viscosity, the flow range and the pressure. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

DON-H meter type

It is a stainless steel oval wheel flow meter.

DON-H liquids

It is for clean, non-abrasive liquids from low to high viscosity.

DON-H example liquids

Examples are petroleum, oil, grease, fuels, pastes, chemicals and ink.

DON-H displacement principle

It is a positive displacement meter.

DON-H conductivity

The reading does not depend on conductivity.

DON-H pulse resolution

Magnets in the rotors give a high-resolution pulse output.

DON-H inlet run

It needs no straight inlet run or flow conditioning.

DON-H compact installation

This suits tight skid and hydraulic installations.

DON-H pressure and temperature

It handles up to 400 bar and plus 120 degrees C.

DON-S version

The DON-S has special-cut rotors with alternate tooth relief.

DON-S pressure drop

It cuts the pressure drop by about 50 percent above 1000 cP.

DON-H x05 range

The x05 range is 0.5 to 36 l/h.

DON-H x10 range

The x10 range is 2 to 100 l/h.

DON-H x15 range

The x15 range is 15 to 550 l/h.

DON-H x20 range

The x20 range is 1 to 40 l/min.

DON-H viscosity

The viscosity is up to 1000 cP, and higher on request.

DON-H medium temperature

The medium temperature is minus 20 to plus 80 degrees C, and up to plus 120 degrees C with the cooling-fin options.

DON-H low temperature

With FKM Vi 840 O-rings it works from minus 40 degrees C.

DON-H materials

The body, wheels and axes are stainless steel 1.4404 with a carbon graphite bearing.

DON-H O-rings

O-rings are FKM, FKM Vi 840, NBR or FEP-encased.

DON-H connections

Connections are G 1/8 on the x05, G 1/4 on the x10 and x15, and G 1/2 on the x20, with NPT versions.

DON-H pulse outputs

Outputs are a reed switch of 30 VDC and 20 mA, or a Hall sensor push-pull of 8 to 30 VDC.

DON-H electronics options

Options include a dual totaliser, dosing, rate with 4 to 20 mA, and relays.

DON-H recommended filter

Use a filter below 75 micrometres for the x05 to x15.

Meter records for the DON-H

Record the liquid, the range, the O-ring material and the date of each cleaning.

Choosing the right DON-H range

Choose the range from the flow rate and the viscosity of the liquid.

Documents and quotation

The KOBOLD DON-H / DON-S datasheet (edition 1/06-2026) is attached to this page. Browse our Flowmeters category for related instruments, or compare with the KRACHT VC gear flow meter.

For a quotation, send the flow range, viscosity, liquid, pressure and temperature, connection, O-ring material, electronics and output options, and any ATEX requirement.